Method of two shot mold metallizing of polymer components

ABSTRACT

A component is provided that is net shape molded using a polymer to form the core structure and which includes an integrally formed metallized coating or layer on at least one of the exterior surfaces thereof. The process of forming the component includes two-shot molding process wherein a thin layer of metal or the base polymer component is molded, the mold is adjusted and then the remainder of the part is molded. Alternately, an insert molding process may be employed such that after the polymer base part is formed, it may be placed into a mold cavity that is slightly larger than the entire part, thereby allowing substantially the entire exterior surface of the part to be over molded with a molten metal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority from earlier filed U.S. Provisional Patent Application No. 60/672,738, filed Apr. 19, 2005, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to polymer components having a metallic coating on at least one exterior surface thereof. More specifically, the present invention relates to a molded polymer component with a metallic layer on at least one of its exterior surfaces that is entirely formed within the mold cavity before the part is removed from the mold. Further, the present invention is directed to a method of forming a molded polymer part to include a metallic layer about at least one of its exterior surfaces while the part remains in the mold

In the component manufacturing industry, it is highly desirable to form components using the least amount of component handling and the fewest number of steps, thereby increasing the speed and efficiency while reducing the cost at which such parts can be produced. Given these goals, a popular manufacturing process for the formation of components is net shape molding. In the net shape molding process, a molten raw material is placed into a mold cavity such that when the component is removed from the mold it is in its finished form and no further processing is required to complete it. Due to the simplicity of the process, net shape molding is used in conjunction with a wide variety of base materials including polymer resins and various metals.

While the net shape molding process works well for a broad range manufactured components, the difficulty with using a net shape molding process, particularly with polymer materials, is that often other steps are required in order to impart various other desirable properties to the part after the molding step is completed. For example, parts that are utilized in electronic devices often must provide additional functionality such as transferring heat within the device, shielding against the effects of electromagnetic interference (EMI), reflecting radiant energy away from sensitive components within the device and/or reflecting light output such as that from a lamp or a light emitting diode (LED). Accordingly, in the prior art, when a reflective surface was desired, the part often was formed using another manufacturing method such as spinning or machining of metal components or by providing a metallized coating onto the desired surface of a polymer based part thereby requiring additional processing steps beyond the net shape molding process. In either case, the cost of manufacturing the part is dramatically increased.

The preferred method of metallizing a polymer component after it has been net shape molded has several drawbacks. Principally, as was stated above, metallizing dramatically increases the cost and time required to manufacture the part. Generally, metallizing requires that the part, once removed from the mold, be prepared using a chemical bath, subsequently plated using vapor deposition or vacu-plating and then finally clear coated to protect the thin layer of metal that was deposited onto the part. These additional steps introduce a great deal of additional handling of the part before it attains its finished state and result in nearly doubling the cost associated with manufacturing the part. Further, even though the cost of the part is increased dramatically, the coating is highly susceptible to wear, peeling, flaking and scratching, all of which lead to premature failure of the component.

Alternately, in the prior art when a part required enhanced thermally conductive properties, the base polymer resin was typically loaded with highly thermally conductive fillers to enhance the thermal conductivity of the finished part. Such fillers typically include carbon black, carbon fibers, ceramic powders and/or metal flakes. While the thermal conductivity of the polymer is improved by the addition of such fillers, the cost of these conductive fillers is typically quite high and the filler loadings that are typically required in order to attain the desired thermal and electrical conductivity properties also resulted in a dramatic impact on the flexibility and strength of the base polymer resin. Further, due to the difference in density between the filler materials and the polymer resin component, the molded part typically includes a resin rich region at its outer surfaces with a concentration of the filler materials towards the center of the component. This is particularly problematic when trying to increase the electrical conductivity of the part because electrical flux tends to travel over the surfaces of objects, precisely in the region of the part that has the lowest concentration of filler material. Accordingly, it is difficult to produce a part that has a relatively high electrical conductivity using net shape molded filler polymers.

An additional difficulty arises when only a portion of the part requires a metallic surface. In these cases, when using traditional metallizing techniques, the portions of the part that will not be coated must be masked or otherwise protected from the coating process. As can be appreciated this introduces an additional time consuming step in the process of manufacturing the component.

Therefore, there is a need for a component that is formed during the molding process to include at least one selectively metallized surface. There is a further need for a component that is formed during the molding process to include at least one integrally formed metallized surface that is highly durable and resistant to wear. There is still a further need or a process of in mold metallization of polymer components that preserves all of the desirable aspects of the net shape molding process and eliminates the additional steps that are traditionally associated with metallizing.

BRIEF SUMMARY OF THE INVENTION

In this regard, the present invention provides for a component that is net shape molded using a polymer to form the core structure and to include an integrally formed metallized coating or layer on at least one of the exterior surfaces thereof. The process of the present invention is directed to a two-shot molding process wherein either a thin layer of metal or the base polymer component is molded, the mold is adjusted and then the remainder of the part is molded. For the purpose of clarity, for the balance of the disclosure for the process of the present invention will be described in terms of forming the base polymer part first, although clearly a process wherein the metal layer is formed first is also fully enabled within the present disclosure.

In a first embodiment of the method of the present invention, the first step provides for injecting a molten polymer into a mold cavity. Once the polymer material is sufficiently set to allow removal of at least a portion of the mold, a portion of the mold cavity is removed exposing the surface of the part that will receive metallization. A replacement mold surface is brought into place to again close the mold. The interior of the replacement mold surface is configured to leave a thin gap between its interior surface and the surface of the part to be metallized. Once the replacement mold surface is in place, a molten metal material is injected into the mold cavity adjacent the surface of the part to be metallized. The molten metal flows over the surface of the part and bonds to the polymer surface. After the part is cooled, it can be removed from the mold in its finished form.

In an alternate embodiment, after the polymer base part is formed, it may be placed into a mold cavity that is slightly larger than the entire part, thereby allowing substantially the entire exterior surface of the part to be over molded with a molten metal. The result of this process is that when the part is cooled and removed from the molding cavity, a net shape molded part is formed that has polymer core with a metallic layer on at least one of the exterior surfaces thereof.

Further, the present invention is directed to a component part that is formed using the teachings of the present invention. Specifically, the present invention is directed to a component having a polymer core wherein at least one exterior surface of the polymer core is over molded to include a thin layer of metal bonded thereto.

Accordingly, it is a goal of the present invention to provide a method of forming a net shape molded component part that includes at least one integrally formed metallized surface. It is a further goal of the present invention to provide a method of forming a component that includes at least one integrally formed metallized surface that is highly durable and resistant to wear through the use of a traditional net shape molding apparatus. It is yet a further goal of the present invention to provide a process of in mold metallization of at least one exterior surface of a polymer component that preserves all of the desirable aspects of the net shape molding process and eliminates the additional steps that are traditionally associated with metallizing. Finally, it a goal of the present invention to provide for a net shape molded polymer component having at least one exterior surface thereof coated with a metallic material that is applied during the net shape molding process.

These together with other objects of the invention, along with various features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed hereto and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings which illustrate the best mode presently contemplated for carrying out the present invention:

FIG. 1 is a cross-sectional view of a molding die having a first profile filled with polymer for implementing the method of the present invention;

FIG. 2 is a cross-sectional view of a molding die having a second profile providing a gap adjacent the polymer core;

FIG. 3 is a cross-sectional view of the molding die of FIG. 2 with the gap filled with molten metal;

FIG. 4 is a cross-sectional view of a molding die having a first profile filled with metal for implementing a second embodiment method of the present invention;

FIG. 5 is a cross-sectional view of a molding die having a second profile providing a gap adjacent the metal;

FIG. 6 is a cross-sectional view of the molding die of FIG. 5 with the gap filled with molten polymer;

FIG. 7 is a cross-sectional view of a molding die having a first profile filled with polymer for implementing a third embodiment of the method of the present invention;

FIG. 8 is a cross-sectional view of a second molding die having a second profile providing a gap adjacent the polymer core;

FIG. 9 is a cross-sectional view of the molding die of FIG. 8 with the gap filled with molten metal;

FIG. 10 is a cross section of a first embodiment composite formed in accordance with the teachings of the present invention;

FIG. 11 is a cross section of a second embodiment composite formed in accordance with the teachings of the present invention;

FIG. 12 is a cross section of a third embodiment composite formed in accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Now referring to the drawings, the implementation of a first preferred embodiment method of the present invention is shown and generally illustrated in FIGS. 1-3. As was stated above, the method of the present invention is principally directed toward in mold metallization of selected surfaces of molded polymer composite components. More particularly, the method of the present invention is directed to the formation of a net shape molded polymer composite component having a metallic layer about at least one exterior surface thereof. In the context of the present invention, the net shape molding process is a common and well-known process whereby a component part is formed on the interior of a mold cavity wherein the part is in its completed form upon removal from the mold cavity. In this regard, the method of the present invention principally employs a net shape molding process using either a two shot or insert molding technique.

Turning now to FIGS. 1-3 a method of forming a net shape molded component including a metallic layer about at least a portion of its exterior surface is shown. In FIG. 1, a molding die 10 formed from a top half 12 and a bottom half 14 and including a mold cavity 16 therein is provided. The mold cavity 16 has a first interior profile shape. A molten polymer material 18 is then injected into the mold cavity 16 and allowed to at least partially cure. Turning to FIG. 2, it can be seen that once the polymer material 18 has set sufficiently to a point wherein if will retain its shape, a portion (the top half 12 in this case) of the first mold cavity 16 is removed and replaced with another mold component 20 that is configured to form a second interior mold cavity 22 that forms a void 24 adjacent the exterior surface of the polymer 18 that is to receive the metallic layer. FIG. 3 then illustrates that a molten metal 26 is injected into this void 24 against the desired exterior surface of the polymer 18. As the molten metal 26 is injected into the mold cavity 22 to fill the void 24, the heat of the molten metal 26 causes some of the polymer material 18 at the exterior surface of the component to reflow and intermix with the incoming flow of molten metal 26. This reflowing of the polymer 18 creates a strong surface bond between the polymer material 18 and the metallic layer 26 that is molded thereon. The entire polymer 18 and metal 26 composition is then cooled and removed from the mold 10 resulting in a polymer component having a metallic layer about at least one surface thereof.

An important element of the present invention is the selection of a base polymer 18 and a metallic alloy 26 that are well suited for combination in the in mold metallization process. One important criterion in selection of the materials is that the metal 26 and polymer 18 must be selected such that their respective melting points are relatively close to one another. It is preferred that the melting points of the polymer 18 and metal 26 are approximately equal. In the case of a metal 26, the melting point wherein the metal 26 transitions from a solid to liquid state spans only about 1° F. In contract, most polymers 18 have a workable melting range that spans over a wide temperature of between 5° F. and 20° F. Below this range the polymer 18 is typically too viscous to flow into the mold and above this temperature range, the polymer 18 burns. In this context, the melting point of the metal 26 must be selected to fall squarely within the workable range of the polymer material 18 that it is being matched with. If the melting point of the metal 26 is much higher than the melting point of the polymer 18, the polymer 18 part that within the mold 10 would be destroyed as the molten metal 26 is injected. Further, if the melting point of the metal 26 is too low, the polymer surface to be metallized will not sufficiently reflow to allow the metal coating and the polymer part to bond.

In the context of the present invention, a variety of polymer resins 18 are suitable for use and all would fall within the scope of the present disclosure. The most important criterion for selecting a polymer resin 18 material is the ability to select a resin that has a usable molten range that closely corresponds with the melting point of the selected metal material 26 as described above. Suitable polymer resins 18 may include a wide range of thermoplastic and/or theromset resins as well as alloys thereof. More preferably, polymer resins 18 that are particularly suited for use in connection with the present invention include polyphenylene sulfide (PPS), co-polymers of acrylonitrile, butadiene, styrene (ABS), polycarbonate and liquid crystal polymers.

In selecting a base polymer 18, it should also be noted that should a highly thermally conductive component be needed, the base polymer 18 may be filled with any number of thermally conductive fillers such as boron nitride, alumina, metal flakes such as aluminum or copper, carbon fillers to greatly enhance the thermal conductivity of the base polymer and in turn the overall thermal conductivity of the part.

In terms of metal 26 selection, it can be seen that the metal 26 must have a relatively low melting point that falls within the usable range of the base polymer resin 18. While any metal material 26 that meets the requirement of having a melting point which is not greatly higher than the base polymer 18 melting (or setting) point would be suitable, it is particularly preferable that such a metal 26 be a eutectic alloy wherein the melting point of the alloy is lower that the melting point of either of the constituent metal components. Often such low melt metals 26 are alloys formed using Tin, Zinc and/or Antimony. Accordingly, metals 26 that are particularly suited for use in connection with the present invention include Tin-Zinc, Tin-Antimony and Zinc-Antimony alloys, although is should be appreciated to one skilled in the art that any metallic material 26 that meets the requirement of having a melting point which is relatively closely matched to the usable range of the polymer 18 would be suitable.

Clearly, while certain polymers 18 and metal alloys 26 have been referred to by name, the present invention is applicable to any process utilizing the general teachings described herein as they would function equally well with a base polymer 18 and metal 26 selected utilizing the selection criteria provided within the disclosure. Further, various different material combinations as well as end uses for the part manufactured using the disclosure provided still fall within the spirit of the present invention.

Turning now to FIGS. 4-6, an alternate method for implementing the teachings of the present invention is illustrated. In FIG. 4, it can be seen that in this embodiment, a method of forming a net shape molded component including a metallic layer about at least one surface thereof is disclosed wherein a molding die 100 is provided that has a first portion 112 and a second portion 114. The first portion 112 and second portion 114 cooperate to form a mold cavity 116 having first interior profile. Instead of injecting a molten polymer however, a molten metal 126 is first injected into the mold cavity 116. The molten metal 126 is then cooled, causing it to solidify. As can be seen in FIG. 5, a portion of the mold is removed (the upper portion 112 in this case) and replaced with a new molding die 120 that forms a second interior profile 122, which includes a void 124 adjacent the layer of solidified metall 26. FIG. 6 then illustrates that a molten polymer 118 is injected into said the void 124 adjacent the metal material 126. As stated above, the polymer bonds 118 to the metal 126 as it is injected. Finally, the metal 126 and polymer 118 composition is cooled to form a polymer component having a metallic layer about at least one exterior surface thereof.

As can be seen in FIGS. 7-9, a third embodiment of the method of the present invention is demonstrated that wherein it is also anticipated that the net shape molding of the component may be accomplished using an insert molding technique. This method is simply a variation of the method described in the first embodiment. In FIG. 7 it can be seen that a molding die 300 is provided that includes a first cavity profile 316 formed by a first molding die portion 312 and a second molding die portion 314. A molten polymer 318 is injected into the cavity 316 and allowed to at least partially cure. Turning to FIG. 8, the polymer 318 is removed from the first mold cavity 316 and placed into a second molding die 302 having a second interior cavity profile 322 formed by an upper mold portion 320 and a lower mold portion 321 wherein the cavity 322 is slightly larger than said first interior profile 316 in at least one dimension forming a gap 324 around at least a portion of the polymer 318 part. Finally, as is shown in FIG. 9, a molten metal 326 is injected into the second mold cavity 322 around at least a portion of the polymer 318 forming a metal layer 326 adjacent the exterior surfaces thereof. Once the polymer 318 and metal composition 326 is cooled it is removed from the mold as a polymer component having a metallic layer about at least one surface thereof. In this embodiment, the second cavity 322 can be formed to allow the metal 326 to flow around and entirely cover the exterior surface of the polymer 318. Alternately, the polymer 318 may be stabilized within the mold cavity 322 in a manner that allows the metal 326 only to flow around selective exterior surfaces of the polymer 318.

The resultant part that is created using the method of the present invention includes a metallic outer surface 26 that is well bonded to the surface of the polymer base component 18 and is highly resistant to scratching. Due to the thickness of the metallic surface 26 it is of particular note that the surface is highly resistant to scratching. When tested utilizing the known prior art testing processes for determining the durability of traditional metallized surfaces, the components manufactured using the teachings of the present invention exhibited no evidence of peeling, flaking or scratching. Of particular note is the fact that the metallic coating 26 on the component exhibited durability and wear characteristics associated with those of the base metal itself. These unique durability and strength characteristics are possible because the outer metallic layer 26 is formed by flowing the molten metal adjacent an exposed surface of the polymer core 18 causing some the polymer material 18 at the surface of the component to reflow thereby creating a linked bond between the polymer 18 and the metallic layer 26. This is in contrast to prior art methods where the metallic material is simply sprayed on without the highly advantageous linked bond of the method of the present invention.

There are other variables that must be considered, as they may affect the process and the resultant component of the present invention, but are not required limitations within the process itself. Principally, this variable is related to the thickness of the metallic coating layer 26. Preferably, the metallic layer 26 is around 0.010″ in thickness. However, the thickness of the metal layer 26 can range from about 0.005″ to any desired overall thickness. This 0.005″ lower limitation results because if the metal layer 26 becomes too thin, the metal 26 tends to freeze too quickly, thereby preventing the mold cavity from fully filling.

Accordingly, the method of the present invention can be seen to create a net shape molded part as shown in FIGS. 10, 11 and 12. FIG. 10 shows a composite part 400 that includes a metallic coating 402 or layer on one exterior surface of the polymer core material 404. Similarly, FIG. 11 provides for composite component 500 that includes a metal coating layer 502 on at least a portion of several of the outer surfaces of the polymer core 504. Finally, FIG. 12 illustrates a composite component 600 that has a metallic layer 602 surrounding the entire exterior surface of the polymer core 604. In any of these embodiments, the present invention provides for a net shape molded component 400, 500, 600 having a complex geometry with a metallized coating 402, 502, 602 that could only be obtained in the prior art by the expensive and lengthy metallization process. The in mold metallized part of the present invention exhibits greatly improved durability as compared to parts formed using prior art methods while also providing a dramatic decrease in time and cost associated with forming such parts. It is anticipated that parts formed using the present invention would be suitable for use in any variety of electronics application wherein heat transfer or EMF shielding are required as well as in any other application wherein a metallized polymer component would be useful for either functional or decorative purposes. Further, the selective nature in which the metallic layer is applied permits the component to be formed to include electrical vias, circuit paths and selective heat transmission paths having complex geometries. For these reasons, the instant invention is believed to represent a significant advancement in the art, which has substantial commercial merit.

While there is shown and described herein certain specific structure embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims. 

1. A method of forming a net shape molded component including a metallic layer about at least one surface thereof, comprising the steps of: providing a mold cavity having a first interior profile; injecting a molten polymer into said mold cavity; partially curing said molten polymer; adjusting said mold cavity to a second interior profile, said second interior profile forming a void adjacent at least one surface of said polymer; injecting a molten metal into said void; and cooling said polymer and metal composition to form a polymer component having a metallic layer in communication with at least one surface thereof.
 2. The method of claim 1, wherein a melting point of the polymer and a melting point of the metal are approximately equal to one another.
 3. The method of claim 1, wherein said metal is a eutectic alloy.
 4. The method of claim 1, wherein said metal is an alloy of metals selected from the group consisting of zinc, tin and antimony.
 5. The method of claim 1, wherein the polymer is selected from the group consisting of thermoplastic polymer resins and thermoset polymer resins.
 6. The method of claim 5, wherein the polymer resin is selected from the group consisting of: polyphenylene sulfide (PPS), polycarbonate, liquid crystal polymers, co-polymers of acrylonitrile, butadiene, styrene (ABS) and mixtures thereof.
 7. The method of claim 1, wherein said step of injecting metal causes said at least one surface of said polymer to partially reflow and bond with said metal.
 8. A method of forming a net shape molded component including a metallic layer about at least one surface thereof, comprising the steps of: providing a mold cavity having a first interior profile; injecting a molten metal into said mold cavity; cooling said molten metal thereby causing it to solidify; adjusting said mold cavity to a second interior profile, said second interior profile forming a void adjacent said solidified metal; injecting a molten polymer into said void; and cooling said polymer and metal composition to form a polymer component having a metallic layer in communication with at least one surface thereof.
 9. The method of claim 8, wherein a melting point of the polymer and a melting point of the metal are approximately equal to one another.
 10. The method of claim 8, wherein said metal is and eutectic alloy.
 11. The method of claim 8, wherein the polymer is selected from the group consisting of thermoplastic polymer resins and thermoset polymer resins.
 12. A method of forming a net shape molded component including a metallic layer about at least one surface thereof, comprising the steps of: providing a first mold cavity having a first interior profile; injecting a molten polymer into said mold cavity; partially curing said molten polymer; removing said polymer from said first mold cavity; placing said polymer into a second mold cavity having a second interior profile that is slightly larger than said first interior profile; injecting a molten metal into said second mold cavity around at least a portion of said polymer; and cooling said polymer and metal composition to form a polymer component having a metallic layer in communication with at least one surface thereof.
 13. The method of claim 12, wherein said metal fully surrounds an exterior surface of said polymer.
 14. The method of claim 12, wherein said polymer is positioned within said second mold cavity such that said metal partially surrounds an exterior surface of said polymer.
 15. The method of claim 12, wherein a melting point of the polymer and a melting point of the metal are approximately equal to one another.
 16. The method of claim 12, wherein said metal is a eutectic alloy.
 17. The method of claim 12, wherein the polymer is selected from the group consisting of thermoplastic polymer resins and thermoset polymer resins.
 18. A net shape molded component, comprising: a polymer core having an exterior surface; and a metal layer molded about at least a portion of said exterior surface of said polymer core, said metal layer having a melting temperature that is approximately equal to a melting temperature of said polymer core.
 19. The net shape molded component of claim 18, wherein said metal layer upon molding around said exterior surface of said polymer causes a portion of said exterior surface to temporarily reflow resulting in a bond between said metal and said polymer.
 20. The net shape molded component of claim 18, wherein a melting point of the polymer and a melting point of the metal are approximately equal to one another.
 21. The net shape molded component of claim 18, wherein said metal is a eutectic alloy.
 22. The net shape molded component of claim 18, wherein the polymer is selected from the group consisting of thermoplastic polymer resins and thermoset polymer resins. 